There are many instances in which multiple electrical loads are connected to and powered by a single, common electrical power source. The common power source may be designed to provide sufficient power for all of the electrical loads, to ensure that each load is adequately powered.
In certain circumstances, though, it may be desirable to provide power to a number of electrical loads from a power source that does not supply enough power to adequately power all of the electrical loads. Requesting more than the available power may in some cases lead to inadequate device performance as well as, or in addition to, activation of protection circuitry built into the power source. For example, an overload can result due to a circuit breaker tripping, an over-current or current limiting circuit causing a power source voltage fold-back, or other method of limiting the distributed power to a known acceptable level without exceeding the source power available. Activation of the protection features can lead to reduced or no power reaching the electrical load(s) that needs powering. Consequently, the functionality of the load(s) attached to the power source can be reduced or disabled.
Source power might be limited for a number of reasons, including, for example, the size of wiring, circuit breaker limits, National and International Electrical Codes, development of harmonic currents, vehicle electrical power limits, or limits stemming from currently available alternative energy sources such as solar or wind-generated power.
One example of an arrangement that may be subject to these types of limitations is a computer notebook or laptop charging cart or charging station. There are many situations in which multiple laptop computers are simultaneously used. For example, multiple laptop computers are widely used in classrooms for educational purposes. In many cases, 10-40 notebooks are simultaneously used in the classroom. Typical laptop carts are cabinets with shelves for the laptops to rest on and power and/or communication connections for charging and/or using the laptops.
In many cases the power consumption required to simultaneously charge and/or use many notebooks can exceed the limits set forth by the National Electrical Code and foreign equivalents for alternating current (AC) line voltages. This type of power consumption may also often exceed the capacity of a direct current (DC) power source that provides the bulk charge current for the electronics that charge notebook batteries directly. Known charging methods require a user to manually switch power between groups of notebooks or batteries to keep the peak current draw within the limitations of the physical configuration. If computer carts or charging stations are provided with auxiliary power take-offs, known methods also require the user to manually switch on any external devices to be powered while internal devices are switched off.